Hi there
Headfirst
EJB by Kathy Sierra and Bert Bates (This book is fantastic and should easily see you through the SCBCD exam with good score.) The book is mainly oriented towards SCBCD and covers all objectives of the exam. If you have more time and want to know more about EJBs
you should refer few chapters from Mastering EJB2 by Ed Roman. The book is freely downloadable in pdf format from
http://www.theserverside.com. Remember to download 2nd edition which addresses EJB 2.0 specification.
Here is the link for
SCBCD resources.
Use EJB 2.0 Specs for reference it will definitely help but not really required.
There are free mock exams available on ejbcertificate.com which are quite useful.